DE102006007437A1 - Electric machine with a device for preventing harmful bearing currents and corresponding method - Google Patents

Abstract

It should be avoided that damaging lubricating film discharges occur on electrical machines via bearings (WL). For this reason, it is planned to use a current source (IQ) to specifically impress a current through the bearing (WL). The current then flows from one of the two bearing components via the lubricating film to the other bearing component. In particular, alternating currents are suitable for making the lubricating film conductive, so that the capacity defined by the lubricating film cannot or only slightly charge.

Description

The The present invention relates to a device for avoiding harmful bearing currents in an electrical machine as well as an electric machine, which is equipped with such a device. Furthermore The present invention relates to a corresponding method to avoid harmful Bearing currents.

aim It is as far as possible to lubricate film discharges in warehouses avoid, as they occur for example in stored steam or gas turbine rotors can. With these runners namely by the friction of the fluid jet on the blades an electrostatic Charging. About that addition, the bearings of transmissions, piston engines or other mechanical, rotating machines are protected. Furthermore, in the case of variable-speed machines, harmful bearing currents are in principle intended be avoided.

Adjustable speed Engines are becoming predominant today powered by voltage source converters. The feed through the voltage source inverter leads to storage currents in the Storing the engine. These bearing currents can vary depending on the design of the Motors lead to premature failure of the bearings. The failure is due to a corrugation on the treads of the bearing (vibrations, noises) or a decomposition of the bearing grease.

Around Bearing currents, so-called circular streams, To prevent, are often isolated power storage, z. B. bearings with ceramic insulation on the outer ring or inner ring, used. Alternatively, hybrid bearings with steel rings and ceramic rolling elements used to avoid circular and EDM currents. These bearings However, they are very expensive and therefore avoided as much as possible. Furthermore are to avoid bearing currents solutions known in which the rotor is grounded with grounding brushes. The grounding brush is subject however, wear and tear the contact security is not given, especially under difficult Environmental conditions. Furthermore, by the company Rockwell in an "Industry White Paper "with the title "Inverter-Driven Induction Motors Shaft and Bearing Current Solutions "proposed between Rotor and stator make a special shielding. Furthermore are in this context also inverters with special pulse pattern for reducing the bearing currents known. All these solutions is common that they are relatively expensive or costly are.

The Object of the present invention is thus to provide an electrical To propose machine, in which the problem of bearing currents on simplified Way solved is. About that In addition, a corresponding method should be specified.

According to the invention this Task solved by an electrical machine with a first active part, a second Active part, which interacts magnetically with the first active part, and a bearing device, with which the active parts are mounted together, wherein the first active part is connected to a first bearing component is, the second active part connected to a second bearing component and a lubricating film separates both bearing components, and a power source connected to the storage facility directly or indirectly connected such that of a bearing component to the other over the lubricating film a targeted current is passed. The word "active part" is used in the present document a stand or rotor of a rotating electrical machine, as well the primary part or secondary part a linear motor understood.

Furthermore is provided according to the invention a method for avoiding harmful bearing currents in one Bearing an electrical machine, the two mutually movable bearing components are separated by a lubricating film, by impressing a targeted electricity, by one of the two bearing components on the Lubricating film flows to the other bearing component.

By the energization of the invention Lubricating film can be in the electrical machine commercial bearings use where previously expensive hybrid bearings were required. Without the harmful Bearing current increased the service life of the bearing is clear.

at a preferred embodiment According to the present invention, the electric machine has Casing, with which one of the two active parts is electrically connected, wherein the power source for introducing the current into the storage facility with the housing connected is. This makes it possible, for example, an electric machine with a power source according to the invention retrofit, without to change the electrical machine inside it.

Preferably shapes the Power source an alternating current in the storage facility. Its frequency should be over 9 kHz for effectiveness reasons lie. This allows the electrical properties of the lubricating film Effectively influence that a certain conductivity is guaranteed, which allows a discharge.

Preferably, the electrical machine has a regulator device, with which the current source so it can be regulated that the electrical voltage between the two bearing components is essentially zero. Thus, it can be achieved that the current passed through the lubricating film is sufficiently high, but it is still not so high that the lubricating film is replaced.

The Power source can be electrically contactless with the storage device be connected. This has the advantage that the moving active part not with a special Kontaktinrich device, z. As contact brushes contacted must become. In a further favorable embodiment the present invention, the power source within the housing with connected to the storage facility. That way too protect the power source or its contact devices from environmental influences.

The Current source advantageously obtains its energy from the terminal voltage of the motor. Thus, there is no special power supply for the current supply of the warehouse necessary.

The inventive power source can also be integrated in a motor encoder. In this way let yourself the entire control electronics of the electric machine compact sum up.

The The present invention will now be described in detail with reference to the accompanying drawings, in which: show:

1 a diagram of a powered with a voltage source inverter in two-point circuit engine;

2 a sectional drawing by an engine;

3 a single-phase equivalent circuit of the motor of 2 ;

4 the engine of 2 with electrical wiring;

5 the wiring of 4 corresponding equivalent circuit diagram with Lagerstromsignalformen;

6 an inventive wiring of a motor with a power source between the shaft and housing and

7 the engine of 6 with regulated current source.

The below described embodiments represent preferred embodiments The present invention is basically Invention applicable to any type of electrical machinery, at which active parts move against each other and the active parts together are stored. In particular, there are advantages in rotating electrical machines, whether runner or stand-fed, independently from the supply with alternating or direct current.

The cause of inverter-related bearing currents is the so-called "common-mode voltage" or "common-mode voltage" in the pulse pattern of the voltage source converter UR, which in 1 is shown. The voltage applied to the motor DM common mode voltage U _o can be z. B. in a star connection of the motor windings between star point and motor housing measure directly. The electronic switching elements SE of the voltage source converter UR connect the voltage U _{d of} the intermediate circuit ZK to the motor windings MW according to a control method. One distinguishes between so-called online and offline control methods. Regardless of the control method used, a fundamental voltage curve U _o results at the star point SP according to FIG 1 , This voltage curve results from the likewise in 1 plotted voltages U _LL between the phases.

The switching on and off of the electronic switching elements SE leads to a voltage change to the parasitic capacitances in the motor and thus to a current flow. 2 shows these parasitic capacitances in a stator-fed AC motor DM, which comprises a stator ST and a rotor RO. The shaft WE of the rotor RO is z. B. stored on roller bearings WL on the stator ST. The voltage U is applied to the windings WI of the stator ST.

This engine construction (see also 3 ) leads to a capacitance C _wh between the motor winding and the motor housing, a capacity C _wr between the motor winding and rotor, a capacity C _rh between rotor and motor housing, an effective capacitance C _b between rolling elements and bearing rings, a nonlinear resistor Z _{n of} the lubricating film and a effective resistance R _{b of} the bearing, consisting of bearing rings and rolling elements.

From these electrical quantities results in in 3 reproduced single-phase equivalent circuit diagram of a three-phase motor including the electrical equivalent circuit diagram for the impedance Z _{b of} the rolling bearing WL. Accordingly, the capacitance C _wh lies between the phase U and the earth PE. Parallel to this capacitance C _wh , a series connection of the capacitances C _wr and C _{rh is} arranged. Again, parallel to the capacitance C _rh is the bearing impedance Z _b . This bearing impedance Z _b consists of a parallel connection of the capacitance C _b and the lubricating film resistance Z _n , which with the bearing resistance R _b in Se switched on.

Harmful bearing currents can be caused by discharge effects. In doing so (cf. 4 and 5 ) the capacity of the rolling bearing C _b charged via the capacitive voltage divider consisting of C _wr , C _rh and C _b , as long as the lubricating film can isolate this voltage. Upon reaching the breakdown voltage, the capacitance C _{b is} short-circuited inside the storage and the capacitance C _rh discharges in this short circuit. As long as the lubricating film is isolated, the voltage across the bearing is an image of the common mode voltage corresponding to the gear ratio BVR (bearing voltage ratio) given by the motor design.

The gear ratio BVR is given by the ratio of the voltage U _Zb at the bearing impedance Z _b and the voltage U _Cwh at the capacitance C _wh . This ratio is typically between 0.02 and 0.2. In 7 For _example , the voltage U _{Zb is} indicated for a small value of BVR and a large value of BVR in its course. In this case, the circuit or the motor winding _is supplied via an impedance Z with half the intermediate circuit voltage 0.5 U _d , which has the same waveform as the voltage U _Zb .

With an inventive, in 6 illustrated circuit IQ a harmless for the bearing WL current I _{b is} coupled, which breaks through the lubricating film of the bearing WL. In this case, the lubricating film forms in connection with the 3 and 5 mentioned capacity C _b . The current I _hf produced by the current source IQ thus flows as a bearing current I _b through the bearing WL, ie the capacitance C _b , but also to a proportion over the capacitance C _rh between the machine rotor RO and the housing or stator ST.

The current I _b causes a short circuit of the lubricating film and prevents the charging of the capacitance C _b . This excludes bearing-internal lubricant discharge currents, and the transmission ratio BVR becomes practically zero. The injected current I _hf is preferably an HF current with a frequency> 9 kHz. However, this preferred frequency may change with the composition of the lubricating film.

The current source IQ not only feeds the current through the lubricating film of the bearing WL, but also absorbs the energy that is coupled through the switching operations of the frequency converter (not shown) via the capacitance C _wr .

In addition to that added here, that the power source as a voltage source with internal resistance accomplished can be.

According to a particularly preferred embodiment of the invention provides according to 7 a controller RE the current of the controlled source in this case IQ so that the bearing voltage U _Zb is regulated despite the coupled energy over the capacity C _wr to zero. The actual value of the controller RE is tapped for example via a low-pass filter TP from the output of the source or directly to the rotor RO and the output voltage U _{a of} the controller RE controls the size of the current I _hf . This results in a regulated current source GI to avoid harmful storage currents.

The Source IQ is contacted, e.g. B. slip rings or contactless over a suitable coupling device, for. As an antenna, to the rotor RO coupled. The coupling of the HF power source can be at any Place of the runner RO done, either inside the engine, to a radiation of the Minimize RF signals, or from the outside on the motor shaft WE.

The Energy for The operation of the HF current wave IQ can be calculated from the terminal voltage of the Motors are won. Alternatively, the RF power source can also its own power supply, z. B. DC 24 V, received. The whole Lighting circuit, here the regulated power source GI or the simple Current source IQ, can also be part of a motor encoder or like running one be.

Claims (13)

Electric machine with - one first active part (ST), - one second active part (RO), which with the first active part (ST) magnetic interacts, and - one Storage facility (WL), with which the active parts (ST, RO) to each other are stored, wherein the first active part (ST) with a first bearing component connected, the second active part (RO) with a second bearing component is connected and a lubricating film separates both bearing components, marked by - one Power source (IQ) connected to the storage facility (WL) directly or indirectly is connected such that from one bearing component to the other on the Lubricating a targeted current is conductive. Electric machine according to claim 1, comprising a housing, electrically connected to one of the two active parts (ST, RO) is, wherein the current source (IQ) for introducing the current in the Bearing device (WL) is connected to the housing. An electric machine according to claim 1 or 2, wherein the current source (IQ) an alternating current in the storage facility impresses. Electric machine according to claim 3, wherein the frequency of the AC over 9 kHz is. Electric machine according to one of the preceding Claims, which has a control device (RE), with which the current source (IQ) is so variable that the electrical voltage between the two Bearing components is essentially zero. Electric machine according to one of the preceding Claims, the current source (IQ) being contactless with the bearing device (WL) electrically connected. Electric machine according to one of claims 2 to 6, wherein the power source (IQ) within the housing with the bearing means (WL) is connected. Electric machine according to one of the preceding Claims, where the current source (IQ) gets its energy from the terminal voltage relates to the electrical machine. Electric machine according to one of the preceding Claims, wherein the current source (IQ) is integrated in a motor encoder. Method for avoiding harmful bearing currents in one Bearing (WL) of an electric machine, the two mutually movable Bearing components are separated by a lubricating film, marked by - memorizing one targeted electricity, by one of the two bearing components on the Lubricating film flows to the other bearing component. The method of claim 10, wherein an alternating current is impressed in the two bearing components. The method of claim 11, wherein the frequency of the AC over 9 kHz is. Method according to one of claims 10 to 12, wherein the impressed current is regulated so that the electrical voltage between the two Bearing components is essentially zero.